Artur Mas, the leader of Catalonia, has a clear message for Madrid: He is serious about his threat to let the people of Spain’s most economically powerful region decide for themselves in a referendum whether they should remain a part of Spain.

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That kind of posturing has thrust Mr. Mas, 56, to the forefront of Spanish politics and made Catalonia the biggest domestic headache for Prime Minister Mariano Rajoy, who is facing troubles on all sides as he tries to satisfy demands from the European Union to straighten out Spain’s economy and from Spain’s heavily indebted regions, including Catalonia.

The question now for Mr. Rajoy, and for all of Spain, is just how far Mr. Mas, a once relatively obscure politician who was elected regional president two years ago, is willing to go in posing what may be the most serious challenge to a sovereign entity in Europe since the implosion of Yugoslavia in the 1990s.

Mr. Mas’s talk is not idle. With a $260 billion economy that is roughly the size of Portugal’s, an independent Catalonia and its 7.5 million inhabitants — 16 percent of Spain’s population — would rank ahead of a dozen of the 27 nations in the European Union. But like most of Spain’s regions, it is under great financial pressure and would like a better deal from Madrid.

In that respect, his threats may amount to nothing more than brinkmanship, as he applies to Madrid much the same tactic it has used to gain favorable treatment in its own dealings with Brussels: that is, that Catalonia, which has its own language and sense of identity, is simply “too big to fail” without calamitous consequences that no one wants to see. On Friday, Catalonia’s government raised the pressure, saying it would not be able to meet its September payments for basic services like heath care on schedule.

For a somewhat more comprehensive take on the uptick in regionalism and the rise of new independence movements in Europe, see the New York Times.